// 函数类型接口，定义一个调用签名，包含参数列表和返回值
(() => {
    interface SearchFunc {
        (source: string, subString: string): boolean
    }
    let searchStr: SearchFunc
    searchStr = function (source: string, subString: string): boolean {
        return source.search(subString) > -1
    }
    console.log(searchStr('888','6666'));
})()